A conventional system for switching optical signals in wavelength division multiplexing has been described on pages 1500 to 1510 of "IEEE Journal on Selected Areas in Communication, Vol. 6, No. 9". This conventional switching system can be applied to a data transmission system in an optical network system by using wavelength division multiplexing disclosed therein.
Such a data transmission system (defined "a first conventional system" hereinafter) may be realized by comprising transmitters on a transmitting side each having a tunable wavelength electric to optical converter, an optical star coupler for combining light signals of different wavelengths transmitted from the transmitters, receives on a receiving side each receiving an optical signal of a fixed wavelength, transmitters on the receiving side each transmitting a state of a corresponding receiver among the receivers on the receiving side, an optical star coupler for combining optical signals transmitted from the transmitters on the receiving side, and receivers on the transmitting side each having a tunable wavelength filter.
In operation, a transmission wavelength of a tunable wavelength filter of one transmitting side receiver is set to be a wavelength of one receiving side transmitter corresponding to one of the receiving side receivers. Then, it is confirmed that the receiving side receiver has not been receiving any optical signal from other transmitting side transmitters, and, if not, a wavelength of a tunable wavelength electric to optical converter of one transmitting side transmitter is set to be a wavelength of a fixed wavelength filter of the receiving side receiver, so that optical communication starts between the transmitting side transmitter and the receiving side receiver.
Another conventional system for switching light signals using wavelength division multiplexing has been described on pages 7 to 13 of "Proceedings of International Switching Symposium", Vol. III". This conventional switching system using wavelength division multiplexing can also be applied to a data transmission system in an optical network system disclosed therein.
Such a data transmission system (defined "a second conventional system" hereinafter) may be realized by comprising transmitters each having a fixed wavelength electric to optical converter, an optical star coupler for combining optical signals transmitted from the transmitters, receivers each having a tunable wavelength filter, and a token ring for setting wavelengths of the tunable wavelength filters of the receivers.
This network has two control phases during a transmission cycle. In the first control phase, the transmitter side ports write information to the tokens indicating to which receiver ports their data are to be sent. The receiver ports read the tokens, and tune their receivers to the appropriate transmitter port wavelength during the second phase.
Then, optical signals transmitted from the transmitters are combined in the optical star coupler, and each or some of the light signals multiplexed in the optical star coupler are received in the receivers by setting the tunable wavelengths of the tunable wavelength filters to correspond with the appropriate transmitted wavelength.
However, the first conventional data transmission system has a disadvantage in that an optical star network system using an optical star coupler, by which the receiving side receivers are checked as to whether they receive light signals from the other transmitting side transmitters or not, must be provided because of the adoption of media-access control.
Further, the second conventional data transmission system has also a disadvantage in that a token ring system, by which wavelengths of the tunable wavelength filters of the receivers are set to be corresponding wavelengths, must be provided because of the adoption of media-access control.